Coupling device



D. M. LOWE COUPLING DEVICE April 8, 1952 Filed May 26, 1943 Qwuwvtoi DONALD M. LOWE Patented Apr. 8, 1952 UN ETED STATES QFF'ICE -ATE.NT

1 Claim.

(Granted under the act of March 3, 1883, as amended April 3t), 1928; 379 Q. G. 757) This invention relates to a means for coupling a concentric line to a multiconductor parallel line.

It i an object of this invention to provide such a coupling means which will make it possible to obtain a greater degree of coupling than has hitherto been possible.

It is a further object to provide such a means which reduce to a minimum the mismatching of impedance at the junction between the lines.

Reference is now had to the drawings in which:

Fig; 1 is a plan view of the coupling means looking axially from the direction of the multiconductor parallel line, and

Fig. 2 is'a section on line 2-2 of Fig. 1.

As shown more clearly in Fig. 2, the invention involves means for coupling a concentric transmission line such as indicated by the reference numeral ill, having an outer cylindrical conductor H and an inner cylindrical conductor l2, with a multioonductor parallel line such as indicated by the reference numeral I 3 and composed of the symmetrically arranged and equally spaced conductors [4; The conductors l t, in known manner, may constitute a multiple parallel line leading either from a high frequency source such as a ring oscillator, or to a balanced multiple load such as a transmitting antenna.

Such a coupling has previously been made by means of a short circuiting plate such as indicated at l5, which conductively and rigidly receives the ends of the conductors M in holes formed for the purpose and is conductively and rigidly secured to the upper end of the conductor II which fits snugly into a hole formed in the center of plate I5. The coupling was completed by extending the central conductor above the plane of the plate [5 and conductively connecting it to alternate ones of the conductors l 4 by means of a spider such as the spider l5 but without enlargement of the central conductor as shown at [1. Each of the ends of the spider had a hole formed therein which slidably but conductively accommodated an alternate one of the conductors M.

This structure enabled the spider to be adjusted vertically with reference to the plate 15. In the use of such a structure, for example in a case where the conductors l4 lead from a ring oscillator, raising the spider reflects a lower load impedance into the oscillator, while lowering the spider reflects a higher load impedance. However, in such known construction, there is the disadvantage that in raising the spider in order to increase the output from the oscillator, there accrue undesirable effects by way of an unbalance between the generator elements of the ring oscillator before the expected output can be obtained.

While satisfactory for certain uses, it was found that the degree of coupling whichcould be obtained by such a construction without a detrimental mismatch of impedance at the coupling, was limited.

In seeking to overcome this limitation, it was discovered that a substantial improvement could be made by regarding the circle of parallel conductors between the plate l5 and spider It as forming a sheath equivalent to the outer conductor of a concentric transmission line. Then by providing a proper ratio of diameters or radii of the protruding portion of the inner conductor i2 between the plate I5 and spider I6, and the circle of conductors la, a higher degree of coupling could be obtained without introducing a detrimental mismatch into the line.

With the arrangement of the present invention, raising the spider reflects a lower load impedance on to the oscillator while lowering refleets a higher load impedance, as before, but with the improvementthat the tendency to effect the unbalance mentioned above is substantially reduced enabling the rated output of the oscillator to be more closely approached.

In accordance with the invention, the portion of the inner conductor I 2 which extends above the plate I5 is enlarged in diameter as shown at ll, the enlarged portion being connected with the lower orsmaller portion through a connecting element IQ of conducting material. The enlarged portion is provided with a telescoping section Ill which fits tightly into a central hole formed in the spider I6. The portions [2, IT, IS and I9 thus form the equivalent of a continuous central conduct-or having an enlarged, extensible, end portion. For the purpose of computing the amount of enlargement necessary for the portion of conduotor !2 within the coupling, the circular array of parallel line conductors between the plate 15 and spider It may be regarded as forming a sheath around the inner conductor so that the coupling section may be considered as an extension of the concentric line l2--l 1.

Thus with a specified value of impedance of the concentric line and with a given spacing between the parallel line conductors, the size of the inner conductor of the coupling section necessary for an impedance match may be easily calculated from the formula for the characteristic impedance of a concentric line:

20:15:18 logm To/Ti where 20 is the characteristic impedance of the line, 1") is the inside radius of the outer conductor, and T1 is the outside radius of the inner conductor. In satisfying the above formula, the ratio between the radius of the portion I1|8 and the radius of the surrounding sheath formed by the parallel conductors becomes such that the impedance of the parallel conductor section matches that of the concentric line.

This condition is obtained by making the ratio of the radius of the enlarged portion l'll8 to the effective radius of the circular array of conductors M, equal to the ratio of the outer radius of the inner conductor 22 to the inner radius of the outer conductor H.

A question might be raised as to the validity of regarding the ring of parallel lines as a sheath comparable to the outer conductor of a concentric line, especially since these lines are not at ground potential. This is not, however, believed to cause a serious error in the calculation, so long as the electrical distance between l5 and I6 is less than a quarter wave length, since the potential on the parallel lines is never greater than that on the inner conductor and decreases from this value at the coupling spider l6 to nearly zero at the shorting plate l5. Furthermore, the voltages on adjacent conductors are in opposite phase. For these reasons the conditions over a large portion of the coupling section closely approach those of a concentric line.

The disclosure has been confined to a single embodiment of the invention in which a parallel line having six conductors is shown. However, the invention is applicable to a parallel line having any even number of conductors which may lead either from a high frequency source such as a ring generator or to a balanced multiple load such as a transmitting antenna. The coupling spider will in any case connect between the inner conductor and one set of alternate parallel conclusters.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim:

llieans for coupling a concentric transmission line to a multiple conductor line having six par allel conductor bars equally spaced, from each other and from a central axis of symmetry, said ,coupling means comprising a metal short-circuiting plate to which said parallel conductor bars are connected in a plane normal to said axis oi symmetry, said plate being provided with a central opening in which opening is fitted the outer cylindrical conductor of the concentric line entering the plate from the side opposite the side to which said parallel conductors are connected and terminating at the surface of the side of the plate to which the parallel conductors are connected, a rigid coupling spider plate of substantial thickness within the ring of parallel conductors having three arms extending radially in a plane normal to said axis of symmetry, said arms being provided with cylindrical channels embracing alternate ones of said parallel conductor bars in sliding electrical contact therewith, a relatively large rigid cylindrical conductor fitted tightly into a central hole formed in the spider coaxial with said axis of symmetry, said conductor extending from the surface of the spider toward the shortcircuiting plate, the ratio of the diameter of the said cylindrical conductor to thediametric spacing between the said parallel conductors being equal to the ratio of the diameter of the inner conductor to the diameter of the outer conductor of the concentric line, a relatively large rigid cylindrical connecting element of approximately the diameter of said cylindrical conductor positioned within the ring of parallel conductors coaxial with said axis of symmetry between said short-circuiting plate and said spider, said connecting element being fixedly secured to the end of the inner conductor of the concentric line and tapered to the diameter of the said inner conductor with a concave curved taper, and a second rigid cylindrical conductor forming a fixed extension of said connecting element extending into sliding telescopic connection with said first cylindrical conductor.

' DONALD M. LOWE.

REFERENCES CITED UNITED STATES PATENTS Name Date Page et a1 Aug. 26, 1947 Number 

